1. Effect of HWT (50°C for 45 minutes) on fungal pathogens in vine nurseries

Researcher: F. Halleen

The aim of the study will be to determine the effect of Hot Water Treatment (50°C for 45 minutes) on the occurrence of fungal pathogens associated with grapevine propagation material and nursery vines. The goal is to ensure complete eradication of these harmful pathogens and to prevent re-colonisation.

Grapevine pathogens, negatively affect nursery vines at various stages during the propagation process. Some species, infect nursery vines through infected nursery soils. Other species can already be in the propagation material as latent pathogens as a result of various factors. These infections can cause damage in the nursery since it adversely affects callusing and rooting, or it can cause problems at a later stage once planted in vineyards.

The objectives of this study will be to determine the effect of HWT (50°C for 45 minutes) on the:

  • Survival of fungal pathogens (in vitro);
  • Eradication of fungal pathogens inside propagation material;
  • Eradication of fungal pathogens inside dormant grafted vines.

The knowledge gained from this study can provide local grapevine nurseries, grape growers and the Plant Improvement Scheme with scientifically-based proof of the efficacy of Hot Water Treatment (50°C for 45 minutes) towards the eradication of harmful fungal pathogens.

 

2. Is the poor detection of leafroll in South African rootstocks due to host resistance?

Researcher: G. Pietersen

The objective of this project is to determine whether difficulties in detection of grapevine leafroll associated virus 3 (GLRaV-3) are due to tolerance or immunity of rootstock clones to this virus. This will allow the certification scheme to adopt policies regarding the testing of rootstock material for GLRaV-3.

Grapevine leafroll associated virus 3 (GLRaV-3) does not produce symptoms and is generally considered to be poorly detected by ELISA and PCR in Vitis rootstocks.

In order to successfully control this virus in rootstocks within the Wine Grape Certification Scheme it is extremely important to ensure that rootstock material supplied to the industry is free of this virus. It is therefore imperative to determine whether the poor detection of the virus in rootstocks is due to low levels of virus (tolerant host defence response), and in which rootstock cultivars this is found. It is also important to determine whether, in some instances, the virus is absent due to immunity by the host. Proving immunity to GLRaV-3 would allow these rootstocks to be used in the industry without any need to test that they are GLRaV-3 free.

The objective of this project is to determine whether difficulties in detection of grapevine leafroll associated virus 3 (GLRaV-3) are due to tolerance or immunity of rootstock clones to this virus. This knowledge will allow the certification scheme to provide science-based recommendations regarding the testing of rootstock material for this important virus.

 

3. Wireless sensor network for smart vineyard monitoring and management

Researcher: R. Wolhuter

This project aims to develop the practical deployment and evaluation of an advanced, self-configuring wireless sensor network (WSN) to support advanced viticultural monitoring and management techniques.

Efficient farming is not possible without relevant and up to date information regarding plant stress, imminent disease, soil conditions and many others. Current data acquisition techniques are relatively expensive and tend to be substantially static in deployment. Adaptation to different applications is generally also time consuming and frequently impractical.

This project aims to develop the practical deployment and evaluation of an advanced, self-configuring wireless sensor network (WSN) to support advanced viticultural monitoring and management techniques. A cost effective, flexible, rapidly deployable monitoring network that can deliver fast and reliable plant and crop information will be of great value to precision farming. The system is intended to provide real time, distributed, frequently updated parameter values, at many freely selected locations. This data could be used to monitor a range of plant, soil and environmental conditions to inter alia provide input into irrigation and disease control strategies. It might also be possible to indicate automatic identification of plant health and crop condition by application of machine learning techniques.

 

4. Effect of grapevine leafroll disease on grape composition and wine quality

Researchers: J.T. Burger and E.H. Blancquaert

This pilot project will evaluate GLD for its impact on grapevine physiology, fruit development and wine quality (phenolic, colour and aroma composition), on four cultivars, under South African conditions.

It is generally accepted that grapevine leafroll disease (GLD) has a negative impact on fruit composition and ultimately wine quality. Anecdotal evidence exists on the impact of GLD on grapevine physiology. The extent of the impact remains elusive, as there is great variation and even conflicting reports worldwide. This project is a pilot study to a larger long-term project that will investigate the effects of GLRaV-3, as the main agent of GLD, under controlled conditions. The pilot project will evaluate GLD for its impact on grapevine physiology, fruit development and wine quality (phenolic, colour and aroma composition), under South African conditions. Four commercial wine cultivars (Cabernet Sauvignon, Merlot, Pinotage and Chardonnay) will be included in the study.

The information generated will be useful to wine producers to make strategic decisions regarding the management of GLD’s effects on the vine, fruit and wine quality. It will also aid in determining the economic impact of GLD within their own setting.

 

5. A study to determine the interaction of GLRaV-3 and GVA during transmission

Researcher: A.E.C. Jooste

This study will test, in a controlled environment, if GVA requires GLRaV-3 for transmission by the mealybug vector. Understanding transmission properties has implications for managing disease spread in vineyards.

A recent study showed that Vitiviruses, including GVA, GVF and GVE, were detected in combination with GLRaV-3 in South African vineyards. Little is known about the interactions between these virus species within a host or during insect transmission. Past research indicated that GVA might require the presence of another virus, i.e. GLRaV-3, for transmission. In a recent mealybug transmission experiment GVA was transmitted on its own to healthy Cabernet franc recipient plants from source plants infected with both GLRaV-3 and GVA. This study will test, in a controlled environment, if GVA requires GLRaV-3 for transmission by the mealybug vector. Understanding transmission properties has implications for managing disease spread in vineyards.

 

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